Those who know the greater glider have a vivid way of describing it: like a flying possum crossed with a koala. About the size of a garden-variety possum, but with a looped tail up to 60 centimetres long and membranes that extend from its elbow to its ankle, it is Australia's largest gliding marsupial.

Scientists say it may not continue to be: it is headed for extinction. Two decades ago, greater gliders were abundant up the east coast, but a combination of land-clearing, logging and the rising threat of bushfires linked to climate change has triggered an 80 per cent population crash.

The greater glider is headed for extinction.Credit:Pavel German

Though they can glide up to 100 metres, greater gliders are docile animals. They typically spend their lives within an area of three or four hectares – about the size of a couple of football fields. When danger arrives, as it did in catastrophically in the central highlands on Black Saturday, they have little capacity to cope.

In April, the Victorian government's independent scientific advisory committee recommended that the animal be listed as threatened species. It followed the federal government last year listing it as vulnerable. The Andrews government is expected to formally accept the recommendation this month.

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But documents released in response to a freedom-of-information request show that the Victorian committee's advice went further.

In November, the committee found the threat facing the glider warranted an immediate suspension of logging in parts of the Strathbogie Ranges north-east of Melbourne. Its formal advice, released to the Goongerah Environment Centre and seen by Fairfax Media, says: "The [glider] is in a demonstrable state of decline which is likely to result in extinction."

Noting gliders usually died if all or most of their home range was cleared, and that the Strathbogie Ranges were an important conservation site as populations there were relatively stable, the committee recommended an interim suspension to timber harvesting.

The advice was rejected by the Department of Environment, Land, Water and Planning. The documents show it advised Environment Minister Lily D'Ambrosio​ that neither she nor the department secretary had the power to stop legal forestry. Instead, it recommended considering "feasible low impact zoning changes" decided in consultation with state timber agency VicForests. It is understood the logging went ahead.

Goongerah Environment Centre campaigner Ed Hill said the advice meant the department was telling the government it should listen to foresters over scientists. He said it reflected that senior figures in the department were themselves former foresters.

"There is a really entrenched pro-logging culture in the department that is completely out of step with its responsibility to protect our threatened wildlife," he said.

Environmental Justice Australia lawyer Danya Jacobs said she believed the departmental advice was wrong – that the government did have the power to intervene to protect the glider. She said there were three potential legal avenues, including issuing an interim conservation order under the Flora and Fauna Guarantee Act.

"It's outrageous for the department to pretend the minister's hands are tied," she said.

Ms D'Ambrosio said the government was listening to the experts, and that no timber harvesting was currently taking place in the Strathbogie Ranges. "We will work with the department and VicForests to investigate reasons for the greater glider's decline and ensure that appropriate protections are in place," she said.

Mr Hill said protection efforts should focus on the central highlands and east Gippsland, where populations were weak and logging continued.

He said it was perverse that, under current regulations, logging could be stopped only if 11 gliders were found in an east Gippsland forest. "If there are fewer of them – if you find 10 – apparently it's OK to kill them," he said.